1. Field of the Invention
Electrical cutting machines employing electrically heated wires.
2. Description of the Prior Art
It is known in the prior art to cut sheet plastic and the like by means of electrically heated moving wires which melt the plastic. U.S. Pat. Nos. 2,526,650 and 2,972,669 disclose machines which employ continuous wire loops heated by means of the wire's resistance to an electric current supplied through rollers in contact with the cutting wire. It is difficult to join two ends of a fine wire, such as a Nichrome wire, without producing either a bulge or weak spot at the junction of the two ends. Therefore, it is difficult to produce an acceptable continuously moving heated wire loop of this sort. Furthermore, the method and apparatus disclosed for supplying electrical current to the endless wire loop would severely limit the temperature which could be provided at the cutting point of the wire to the extent that the cutting action would rely upon melting rather than vaporizing the material severed. Thus, the melted plastic tends to recycle into the cut and in effect weld the two sections together again. There are also machines such as that disclosed in U.S. Pat. No. 3,064,111 which employ a long length of fine wire fed in one direction from one spool to a motor driven take-up spool and heated by electrical resistance through two contacts bearing against the wire. After the cutting wire is completely unwound from the feeding spool, the direction of the movement is reversed. Such machines are impractical for cutting material several inches thick where high temperatures would be required as it is not practical to supply the cutting wire with sufficient amperage to sever dense materials because of the difficulty of providing positive electrical contacts with electrodes which slide against a moving wire.
Another machine for cutting sheets of plastic material is disclosed in U.S. Pat. No. 3,259,004 which is a sort of band saw without teeth, heated by friction against the plastic material, or possibly by heating the blade from an outside induction heater, but such machines are suitable for cutting only the most flimsy materials and not for performing fine, clean cuts on sheet plastic or other thicker, denser materials.
Likewise, there is a machine disclosed in U.S. Pat. No. 3,585,889 which cuts plastic material by means of a reciprocating wire but which is heated by the friction generated by the movement of the wire across the surface of the material being cut. It is impractical to generate enough heat by friction for the cutting of various types of sheet plastic material. Also, it would appear that the heat of friction in such a machine would, at most, barely melt the material.